364
Answers to the Quickies
6. Chitosan is obtained on an industrial scale
by alkaline-catalyzed deacetylation of
chitin with concentrated caustic soda lye.
Deacetylation can also be carried out using
certain enzymes, deacetylases, which are
either used directly or formed in situ by
microorganisms.
7. Chitosan is soluble in organic acids. The
solubility is based on the fact that chitosan
forms a polycation below a pH value of 6
in which the free amine functionalities are
protonated. Thus, it is soluble in an aqueous
environment and can be further processed.
8. Chitosan is first dissolved in 1% aqueous
acetic acid, filtered and then added to a
carrier as a solution to form films. This
“chitosan acetate” is then dried. The chitosan is restored with 2% aqueous NaOH.
Afterward, the chitosan is dried again in
air. Chitosan films are used, for example, as
membranes or capsules for drugs.
9. Chitosan forms so-called chelate complexes
with metal cations, in which the central
atom is bound to chitosan via more than
one coordination site. These inclusion
compounds are very stable and can be used
to selectively separate heavy metals from
wastewater.
10. Chitosan is used in cosmetics in skin and
hair care products. It is also used in the
coating of paper or textiles, as a matrix for
chromatography, as a coating agent for seeds
and fruits, as a dietary supplement and as
a coating in the treatment of wounds and
burns.
Answers to 7 Chap. 10
1. Cyclodextrins do not belong to starch
hydrolysates, since the glycosidic bond is
not formally hydrolyzed but reacetalized.
2. Cyclodextrins cannot be produced from cellulose because the glucose building blocks in
cellulose are β-glycosidically linked. To form
the cyclic structure, an α-link is required, as
it occurs in amylose.
3. Cyclodextrin with nine glucose monomers
is called δ-cyclodextrin; it has three free
hydroxyl groups per glucose building block
and thus has a total of 27 OH groups. The
outer dimensions in height do not change
due to enlargement of the ring, which means
that δ-cyclodextrin, like the cyclodextrins
indicated, also has a height of about 780 pm.
The outer diameter changes by about
160 pm as the number of glucose building
blocks increases. Thus, δ-cyclodextrin has an
outer diameter of about 1850 pm.
4. Amylases break glycosidic bonds by
hydrolysis, resulting in shorter, open-chain
fragments of amylose. Cyclodextrin glycosyltransferases “cut” the amylose into pieces
and link the ends to a cycle of six, seven or
eight glucose building blocks. This means
that the glycosidic bond is not hydrolyzed.
5. Cyclodextrins have a hydrophobic cavity in
which apolar substances can be incorporated due to their special three-dimensional
structure. The stability of this inclusion
compound depends, among other things,
on the relative size of the guest in relation to
the corresponding cyclodextrin (host). The
β-cyclodextrin has a cavity into which the
aromatic toluene fits exactly. This inclusion
compound is no longer water soluble under
certain conditions. This can be exploited to
selectively remove β-cyclodextrin from the
equilibrium during enzymatic synthesis,
thus increasing the yield of β-cyclodextrin.
6. Cyclodextrins were first mentioned in 1891
by A. Villier and initially called “cellulosin”.
7. During the formation of an inclusion
compound between cyclodextrins and a
guest molecule, the apolar compound is
protected against external influences such
as oxidation, UV radiation or temperature.
The relative volatility is also reduced and the
solubility in aqueous media is increased.
8. The resulting inclusion compound between
the apolar impurity and the cyclodextrins
is treated with organic solvents such as
alcohols. This results in the apolar substance
being washed out by the large excess of
solvent and the “empty” cyclodextrin being
available again for cleaning purposes.
9. The fatty phase containing cholesterol
is first emulsified at 40 °C with a water
phase containing cyclodextrin. The apolar cholesterol molecule is enclosed in
the cavity of the β-cyclodextrin. The solid
cholesterol-cyclodextrin complex precipi-
Answers to the Quickies
6. Chitosan is obtained on an industrial scale
by alkaline-catalyzed deacetylation of
chitin with concentrated caustic soda lye.
Deacetylation can also be carried out using
certain enzymes, deacetylases, which are
either used directly or formed in situ by
microorganisms.
7. Chitosan is soluble in organic acids. The
solubility is based on the fact that chitosan
forms a polycation below a pH value of 6
in which the free amine functionalities are
protonated. Thus, it is soluble in an aqueous
environment and can be further processed.
8. Chitosan is first dissolved in 1% aqueous
acetic acid, filtered and then added to a
carrier as a solution to form films. This
“chitosan acetate” is then dried. The chitosan is restored with 2% aqueous NaOH.
Afterward, the chitosan is dried again in
air. Chitosan films are used, for example, as
membranes or capsules for drugs.
9. Chitosan forms so-called chelate complexes
with metal cations, in which the central
atom is bound to chitosan via more than
one coordination site. These inclusion
compounds are very stable and can be used
to selectively separate heavy metals from
wastewater.
10. Chitosan is used in cosmetics in skin and
hair care products. It is also used in the
coating of paper or textiles, as a matrix for
chromatography, as a coating agent for seeds
and fruits, as a dietary supplement and as
a coating in the treatment of wounds and
burns.
Answers to 7 Chap. 10
1. Cyclodextrins do not belong to starch
hydrolysates, since the glycosidic bond is
not formally hydrolyzed but reacetalized.
2. Cyclodextrins cannot be produced from cellulose because the glucose building blocks in
cellulose are β-glycosidically linked. To form
the cyclic structure, an α-link is required, as
it occurs in amylose.
3. Cyclodextrin with nine glucose monomers
is called δ-cyclodextrin; it has three free
hydroxyl groups per glucose building block
and thus has a total of 27 OH groups. The
outer dimensions in height do not change
due to enlargement of the ring, which means
that δ-cyclodextrin, like the cyclodextrins
indicated, also has a height of about 780 pm.
The outer diameter changes by about
160 pm as the number of glucose building
blocks increases. Thus, δ-cyclodextrin has an
outer diameter of about 1850 pm.
4. Amylases break glycosidic bonds by
hydrolysis, resulting in shorter, open-chain
fragments of amylose. Cyclodextrin glycosyltransferases “cut” the amylose into pieces
and link the ends to a cycle of six, seven or
eight glucose building blocks. This means
that the glycosidic bond is not hydrolyzed.
5. Cyclodextrins have a hydrophobic cavity in
which apolar substances can be incorporated due to their special three-dimensional
structure. The stability of this inclusion
compound depends, among other things,
on the relative size of the guest in relation to
the corresponding cyclodextrin (host). The
β-cyclodextrin has a cavity into which the
aromatic toluene fits exactly. This inclusion
compound is no longer water soluble under
certain conditions. This can be exploited to
selectively remove β-cyclodextrin from the
equilibrium during enzymatic synthesis,
thus increasing the yield of β-cyclodextrin.
6. Cyclodextrins were first mentioned in 1891
by A. Villier and initially called “cellulosin”.
7. During the formation of an inclusion
compound between cyclodextrins and a
guest molecule, the apolar compound is
protected against external influences such
as oxidation, UV radiation or temperature.
The relative volatility is also reduced and the
solubility in aqueous media is increased.
8. The resulting inclusion compound between
the apolar impurity and the cyclodextrins
is treated with organic solvents such as
alcohols. This results in the apolar substance
being washed out by the large excess of
solvent and the “empty” cyclodextrin being
available again for cleaning purposes.
9. The fatty phase containing cholesterol
is first emulsified at 40 °C with a water
phase containing cyclodextrin. The apolar cholesterol molecule is enclosed in
the cavity of the β-cyclodextrin. The solid
cholesterol-cyclodextrin complex precipi-